This invention refers to chemical dyeing, in particular of polyamide yarns. Chemical dyeing is affected by using acid or anionic dyes that bond chemically to the amino end-groups (primary amines), or to other amine (secondary and tertiary), of the polyamide chains, or basic or cationic dyes, that bond chemically to the carboxyl end-groups, or to other active sites, like sulfonate-groups, of the polyamide chains. The mechanism of Nylon dyeing has been thoroughly investigated and described in “Challenges in the Art and Science of Dyeing” AATCC symposium (No. 32), 1983. The rate of diffusion, hydrogen and ionic bonding of the dyestuff to the polyamide and the dyeing mechanism have been reported. Even small changes in the amino end-groups content may affect the uptake of the acid dyestuff by the yarn in the dyeing bath, and thus affect the depth of the dyeing and the color intensity of the garment. The process of controlling the dyeing depth of Nylon by acid dyestuff via variation in the amino end-group concentration is well known in the art. U.S. Pat. No. 3,511,815 teaches that by obtaining high amine-end group (120-150 meq/kg), the Nylon 6,6 exhibits increased dyeability.
U.S. Pat. No. 4,017,255 describes a process for manufacturing of fiber materials containing at least two groups of differentially dyeable nylon filaments of two types. A first filament type, for cationic dyeing purposes is composed of nylon having content of about 90 to 110 meq per gram of carboxyl end groups and amino end groups content of about 20 to 30 meq per gram. A second filament type, for anionic purposes, which is composed of nylon having content of about 20 to 30 meq per gram of carboxyl end groups and amino end groups content of about 90 to 110 meq per gram. Wherein, the two types of textile filaments can be simultaneously dyed with an anionic and cationic dyestuff.
However, as mentioned in U.S. Pat. No. 3,951,599, U.S. Pat. No. 3,542,473, U.S. Pat. No. 4,017,255 has a drawback, since the carboxyl end-group sites have a limited dyeing strength, i.e. acidity, thus such end groups do not dye optimally by cationic dyeing procedures. The application of cationic dyes, which react with the carboxyl end-groups of the nylon molecules, results in dyed nylon having unacceptable color fastness properties. In other words, it is possible to improve the effective cationic dyeing of the filaments that are described in U.S. Pat. No. 4,017,255, by other formulations. It has also been noted that yarn spinning of PA 6,6 having the high amino end-group content is difficult using normal manufacturing facilities, and they are known for their poor spinning efficiency, i.e. increased occurrence of breaks and drips, most likely due to gel formation.
Nylon has been modified to improve its dyeability with cationic dyes by adding sulfonate compound to the PA 6,6 to provide sulfonate groups which can be activated to react with cationic dyestuff, as described in U.S. Pat. No. 3,142,662, U.S. Pat. No. 3,389,549, U.S. Pat. No. 3,542,743, etc.
U.S. Pat. No. 4,295,329 teaches the use of a first yarn which contains sulfonate sites for cationic dyeing, and of a second yarn which is of regular or deep acid-dyeing capability. This process is suitable for the preparation of heavy denier bulked yarns within the range of 1500-5000 total denier, mostly for carpet applications.
U.S. Pat. No. 3,389,549 teaches that for providing polyamides with cationic dyeing capability, the PA 6,6 should have a level of at least 60 sulfonate equivalents, while amino end groups contents is within 10-30 meq per kg. U.S. Pat. No. 3,542,743 teaches that the sulfonate groups of modified nylon molecules can be activated to react with cationic dyestuff under acidic conditions independently of carboxyl groups. It has been shown that the sulfonate groups can be effectively dyed by cationic dyeing techniques, and they have good light fastness properties. Also, sulfonate groups impart anionic dye-resistant properties to the nylon by forming a salt with amino end groups, thereby rendering these amine groups no longer available to react with anionic dyes. Such yarns, spun from the modified nylon, for example, with sodium salt of 5-sulfoisophthalic acid, dye particularly well by cationic dyestuff, while in the presence of anionic dyestuff, in the same bath.
US Pre-Grant Publication US 2003/0220037 describes an iridescent fabric comprising a cationic-dyeable nylon polymer yarn and an acid-dyeable yarn, which can be dyed in a single bath using an acid dye and a cationic dye. The dyeability of the cationic-dyeable yarn of the iridescent fabric is ensured by providing sulfonate group concentration of about 55 meq per gram polymer, amino-end group concentration of no greater than 40 meq per kg polymer. In this specific formulation there is an insignificant difference in the concentration between sulfonate end groups and amino end groups to affect the cationic dyeability of the sulfonate yean. In the same Publication The deeply dyeing property of the second yarn is provided only for anionic-dyeable nylon yarn using an enhanced level of amine end-groups of about 70 meq per kg polymer. The cationic-dyeable yarn does not have the deeply dyeing property, since there is a relatively low level of sulfonate groups, and significantly high amino-end groups content in the cationic-dyeable yarn prevents the sulfonate groups from being available for cationic dyeing. In summary, although the fabric that described in Publication US 2003/0220037 dyes in two colors simultaneously, the contrast of the colors is not as distinct and sharp as it could be.
U.S. Pat. No. 3,328,431 describes the use of butyrolactone for reducing the number of amino end-groups and British Patent 1,142,297 describes the use of (-caprolactone for the same purpose.
U.S. Pat. No. 4,017,255 teaches a process for the manufacturing of fiber materials containing at least two groups of differentially dyed Nylon filaments, each having a different carboxyl end-group content.
European patent application EP 409,093 teaches a method for reducing the number of amino end-groups by reacting polyamide fibers and combining them with normal polyamide fibers, thus resulting in a two-tone yarn. This process is mainly useful for stain blocking in the carpet industry.
Co-pending patent application 141240, the contents of which are entirely incorporated herein by reference, discloses a process for the manufacturing of a differentially dyeable yarn, comprising the steps of:                producing two polyamides having a different concentration of amine end-groups:        spinning yarns from said two polyamides; and        producing a yarn by intermingling said spun yarns made from said two polyamides, in texturing, or draw twisting, or draw winding processes. Preferably, the two polyamides are made from the same monomer or co-monomers.        
Polyamide yarns, particularly those made from polycapronamide (Nylon 6), polyhexamethylene adipamide (Nylon 6,6), or polyhexamethylene sebacamide (Nylon 6,10) can be used in the textile industry in both knitting and weaving with high efficiency to form high quality and fashionable garments. These polyamides, especially Nylon 6,6, are used in the production of knitted leg-wear and body-wear garment. In these products, dyeing efficiency and cost effective dyeing processes are important considerations.
It is a purpose of the present invention to provide a process for preparing fabrics—woven, knitted or non-woven—having patterns or designs in at least two different colors, which process comprises a single dyeing operation. By “fabrics having patterns or designs in two different colors” is meant herein fabrics which comprise surface areas of a first color and surface areas of a second color, regardless of the shape and positioned relationship of said areas, which may be geometrically simple, such as stripes, or complex, such as intercalated curved shapes or figures in the first color on a background of the second color, and regardless of the technique by which said surface areas are created. The fabrics of the invention are made of polyamide yarns, particularly yarns of poly(hexamethylenediamine-co-adipic acid, (Nylon 6,6), poly(hexamethylenediamine-co-azelaic acid) (Nylon 6,9), poly-(hexamethylenediamine-co-sebacic acid) (Nylon 6,10), or copolymers thereof. Preferably, the different colors are obtainable one from basic (cationic) dyes and one from acid (anionic) dyes.
According to the present art, such fabrics having patterns or designs in different colors are obtained by providing two sets of yarns adapted to be dyed by different dyes, separately dyeing or pre-dyeing said two sets of yarns, and weaving or knitting a fabric from said dyed yarns so as to achieve a desired color pattern and, if the yarns are partially pre-dyed, finishing the final garment with a dyeing process. This is a fairly complex procedure, that requires at least two different dyeing operations or the availability of yarns with different colors, and is therefore expensive, and it limits the economical number of colors and shades that the manufacturer can use in making a textile product.
It is a purpose of this invention to provide a process for the manufacture of a fabric having distinct and sharp differentially colored patterns or designs that is free of the drawbacks of the prior art, or cross staining of the yarns by the other dyes.
It is another purpose of this invention to provide a single-step dyeing process for manufacturing such a fabric that is simple and inexpensive.
Other purposes and advantages of the invention will become apparent as the description proceeds.